Bath and process for chemically nickel plating magnesium



States Unite This invention deals with the problem of nickel platingmagnesium containing articles chemically, or electrolessly.

It is a fact that prior proposals for dealing with this problem haveinvariably met with failure, for one reason, because all known chemicalnickel-plating baths have eflected destructive or unacceptable corrosionof the magnesium being plated. These baths all contain, or are made upwith, water and at even the minimum operating temperatures feasible, forexample, 90-95 C., even the water detrimentally reacts with themagnesium. The presence of the free ions in this heated water bathmaterially augments corrosion, particularly if these ions are theconventional chloride ions derived from NiCl Further, the products ofcorrosion react back on the bath and disassociate its components,breaking the bath down into an ineffective mixture of separatecomponents.

We have discovered that a bath which, among other advances, (1) totallyobviates chloride ions; (2) employs fluorine ions which prevent attackon the magnesium while plating it; (3) operating the bath at a criticalpH range of 9-12, inc., while (4) concurrently employing a reagent whichbuffers the reaction and maintaining the pH constant, and also preventsprecipitation of nickel ions due to this alkalinity of the bath; and (5)operating the bath at a critical temperature range of 9095 C., magnesiumarticles can, for the first time in this art, be satisfactorily nickelplated without possibility of corrosion or other deleterious action.

Several examples of bath-formulation according to the present inventionare set forth hereinbelow but only by way of exemplification of theinventive concepts.

One of the now-preferred formulations of the present bath which has,over a satisfactory period of usage, been found to eliminate theaforestated, and other, defects is as follows:

Gms./liter NiSO .6H O to NaH PO .H O to NH CH COOH 20 to 30 NaF 2 to 10Water suflicient to make up 1 liter is added.

Further, in order to establish the essential alkalinity, a 10% solutionof NaOH or other caustic or base, is added to the foregoing in an amountsuflicient toraise the pH to a range of 9-12, inc. This pH is maintainedstable by the buffer aforementioned, while the NaF protects themagnesium chemically while it is plated by the reduction of thechloride-free nickel salt via the hypophosphite.

It is also preferable that a bath-temperature be maintained that is inthe range of 90 C.-95 C.

This particular bath has been found to deposit nickel on the magnesiumarticle at the rate of substantially 1 mil per hour.

It will be observed that nothing in the nature of the usual preliminarycoating of the magnesium is employed herein.

The nickel plating herein is rather bright, although no discretebrightener is employed. The plating is hard, homogeneous, and dense,lacking any appearance of sponginess. It is quite adherent and does notblister or peel despite exposure to salt air, etc.

atent ice In the aircraft industry, for example, present bath andprocess are eminently well adapted for nickel plating magnesium waveguides and the vital airframe parts of guided, and ballistic, missiles.

In the electronics industry, the invention is sharply advantageous inenabling magnesium parts to be so plated that they can be soldered toother parts.

A second desirable formulation of the bath for electrolesslynickel-plating magnesium containing articles is as follows:

(1) NiSO .6H O, 10 to 20 gms./ liter;

(2) NaH PO .H O, 10 to 30 gms./liter;

(3) NaF, 2-10 gms/liter;

(4) Water to make up 1 liter;

(5) An alkalinizing, complexing and buffering agent like NH OH, in anamount suflicient to raise pH to 9-12 is added and the bath ismaintained at 9 095 C.

The NH OH serves, here, a triple function, acting as (l) a bufferingagent, (2) a nickel-complexing agent, and (3) as a replacement forcaustics as an alkalinizing agent.

A third formulation which has satisfactorily achieved the presentobjectives is composed as follows:

Guts/liter NiCO 10 to 20 H3PO2 to HF 2-10 NH CH COOH 20-30 Water to makeup 1 liter is also employed, while NaOH, or other base or caustic isadded in an amount sufficient to raise the pH to a value of 9-12,inclusive.

Although certain quantities, ratios, volumes and other parameters havebeen set forth hereinabove for the sake of concreteness, it is to beunderstood that the invention is limited, both in fact and at law, onlyas required by the scope of the subjoined claims.

We claim:

1. A process for nickel plating a body that incorporates magnesium,comprising: contacting a magnesium-containing body with a chlorideion-free aqueous solution, at 9095 C., of (1) 10-20 grams per liter of anickel salt that is free of the chloride-ion; (2) 10-30 grams per literof a hypophosphite-ion-containing reducing compound that is free of thechloride-ion; (3) 2-10 grams per liter of an inorganic compound that isfree of chloride ions and incorporates the radical of hydrofluoric acidas its active factor and establishes fluoride ions in aqueous solution;and adding, in an amount per liter of the aqueous solution adequate tocomplex the nickel ions in the solution, buffer the body against freehydrogen ions and alkalinize the solution to pH=9-12, a chemical systemthat is free of the chloride ion and that contain ions which contain theamino group and hydroxyl ions.

2. A process according to claim 1, in which the nickel salt is nickelsulphate.

3. A process according to claim 1, in which the nickel salt is nickelcarbonate.

4. A process according to claim 1, in which the reducing compound issodium hyp'ophosphite.

5. A process according to claim 1, in which the reducing compound ishypophosphorous acid.

6. A process according to claim 1, in which the compound thatincorporates the radical of hydrofluoric acid is sodium fluoride.

7. A process according to claim 1, in which the compound thatincorporates the radical of hydrofluoric acid is ical system thatincorporates amino, including ions and also hydroxy ions, is ammoniumhydroxide.

10. A bath for nickel-plating articles incorporating magnesium,comprising: nickel sulphate, lO20 grams/ liter; sodium hypophosphite,l030 gins/liter; aminoacetic acid, 2030 gms./liter; sodium fluoride, 210gms./ liter; water sufficient to make up one liter of bath; and sodiumhydroxide suflicient to establish a pH of 9-12, inclusive.

11. As a new composition of matter for nickel plating magnesiumarticles: an aqueous solution, free of chlorine ions, of a nickel saltthat is free of the chlorine-ion and is present as 10-20 gms./1iter;10-30 grams/liter of a hypophosphite-ion containing reducing compoundthat is free of the chloride ion; an inorganic compound that is free ofthe chlorine ion, and incorporates the radical of hydrofluoric acid andis present as 21O gms./ liter; and a chemical system consisting ofamino-ions and hydroxy ions, said system being free of chlorine ions andpresent in an amount per liter, based on the amount of nickel ions,hypophosphite ions and fluorine ions present per liter, that is adequateto effectuate complexing of the nickel ions, buffering of the magnesiumarticle against free hydrogen ions and alkalinizing of the solution to apH=9-12, inclusive.

12. A composition according to claim 11, in which the complexing,buffering and alkalinizing system consists of an aqueous solution of H.NH .OH in an amount sufficient to raise the pH of the composition to9-12, inelusive.

13. A composition according to claim 11, in which the chlorine-freenickel salt consists of 10-20 gms. liter of NiCO References Cited in thefile of this patent UNITED STATES PATENTS 2,532,283 Brenner Dec. 5, 19502,694,017 Reschan et al. Nov. 9, 1954 2,694,019 Gutzeit Nov. 9, 19542,886,451 Budininkas May 12, 1959

1. A PROCESS FOR NICKEL PLATING A BODY THAT INCORPORATES MAGNESIUM,COMPRISING: CONTACTING A MAGNESIUM-CONTAINING BODY WITH A CHLORIDEION-FREE AQUEOUS SOLUTION, AT 90-95*C., OF (1) 10-20 GRAMS PER LITER OFA NICKEL SALT THAT IS FREE OF THE CHLORIDE-ION; (2) 10-30 GRAMS PERLITER OF A HYPOPHOSPHITE-ION-CONTAINING REDUCING COMPOUND THAT IS FREEOF THE CHLORIDE-ION; (3) 2-10 GRAMS PER LITER OF AN INORGANIC COMPOUNDTHAT IS FREE OF CHLORIDE IONS AND INCORPORATES THE RADICAL OFHYDROFLUORIC ACID AS ITS ACTIVE FACTOR AND ESTABLISHES FLUORIDE IONS INAQUEOUS SOLUTION; AND ADDING, IN AN AMOUNT PER LITER OF THE AQUEOUSSOLUTION ADEQUATE TO COMPLEX THE NICKEL IONS IN THE SOLUTION, BUFFER THEBODY AGAINST FREE HYDROGEN IONS AND ALKALINIZE THE SOLUTION TO PH=9-12,A CHEMICAL SYSTEM THAT IS FREE OF THE CHLORIDE ION AND THAT CONTAIN IONSWHICH CONTAIN THE AMINO GROUP AND HYDROXYL IONS.